U.S. patent application Ser. No. 09/052,664, now U.S. Pat. No 5,962,568, describes a coating powder based on 100% silicone as the binder system. The silicone resin described therein is particularly formulated for use in a coating powder.
Because silicone polymers are stable above 600.degree. F. (315.degree. C.) where carbon polymers decompose, the binders of current high temperature powder coatings contain a maximum of silicone resins. For example, the binder of coating Mor-Temp Stove Black 99-7020 contains 97.3% silicone resin and 2.7% of various organic compounds, including curing agents, flow modifiers and degassing aids. While such coatings have reasonable adhesion to substrates such as aluminum after exposure to temperatures above 600.degree. F., their adhesion to ferrous substrates is poor after exposure to these temperatures.
Many articles which could potentially be coated with a high temperature powder coating are fabricated from low-carbon steel. Examples are exhaust system components for automotive and non-automotive engines of all sizes, stoves, heaters, barbecue grill and grill components. The adhesion of current silicone systems is not adequate for these applications. Accordingly, the invention is directed to powder coatings which provide a high-temperature coating with improved adhesion to ferrous substrates.
Herein it is found that the addition of a polyhydroxyl component improves adhesion of silicone-based coating powders to ferrous substrates.